1. Field of the Invention
The present invention relates to a golf club head and, more particularly, to a metal golf club head incorporating a hollow portion.
2. Description of the Related Art
Conventionally, when manufacturing the head main body of a metal hollow golf club head by casting, it is generally done by investment casting (lost wax process). When manufacturing the head main body in accordance with this process, an opening must be formed in the head main body so that the core of the mold to form a hollow portion can be extracted through it. Therefore, an opening is formed in the sole portion or face portion. A face plate formed by forging or press molding is fitted in the opening formed, for example, in the face, and fixed by welding, thus forming a golf club head.
When forming an opening in a head main body and fitting a fitted member such as a face plate in the opening, a stopper is provided inside the opening so that the fitted member will not drop into the hollow portion. This facilitates welding of the fitted member to the head main body. As the stopper, a pawl projecting from part of the opening (for example, see Japanese Patent Laid-Open Nos. 2001-259091 and 2001-46559), or a ridge projecting along the edge of the opening may be used.
When forming a pawl or ridge serving as the stopper inside the opening formed in the face portion, as in the conventional case, the pawl or ridge interferes with the face plate's ability to flex and decreases the rebound of the ball. This decreases the traveling distance of the ball.
Particularly, the conventional design as described above is developed under the assumption that the golfer hits the ball with the sweet spot of the golf club head. If the golfer is a general amateur golfer whose hitting point varies largely, it is difficult for him to hit the ball on the sweet spot. When the golfer hits the ball at a hitting point off the sweet spot, the rebound of the ball decreases, and the traveling distance of the ball decreases greatly. Also, the traveling distance greatly changes depending on the hitting point.
Variations in hitting point of general amateur golfers are studied. The hitting points vary within an ellipse as indicated by an area Z in FIG. 5, which has as a major axis a line D that connects the toe-side upper portion to the heel-side lower portion.